Electric-drive vehicles including hybrid vehicles and electric vehicles, for example, are widely used. An electric-drive vehicle includes a battery for supplying electric power to a drive motor. A battery in a hybrid vehicle is charged with electric power generated by driving force of the engine and by regenerative braking. A battery in a plug-in electric drive vehicle is charged with electric power supplied from a commercial power source. In order to charge the battery, the electric-drive vehicle includes a power converter. The power converter converts voltage that is input for charging the battery appropriately and then applies the appropriate voltage to the battery.
JP 2011-193713 A discloses a power converter including two switching circuits magnetically coupled with each other by windings connected to the respective switching circuits for transmitting electric power between the two switching circuits. JP 2010-183726 A discloses a power converter which controls output voltage by adjusting the frequencies of first and second boost converters while improving the power factor of the first and second boost converters based on time ratio modulation.